I loved the atmosphere of danger from Island of Doom and City of the Lost. Regarding serials, The Kingdom, Dark Mirror, and Journey's End were my favorites.
Wow! I have gotten Bionicle and Lego parts for extremely low prices at garage sales, but never anything that just cost a nickel. Once I did get the Toy Story Trash Compactor set (minus a few parts) for $1 though, which normally costs $50.
Just thought of another suggestion - it would be cool if you could buy/sell stuff from the traders. Maybe also collect natural resources like gems and bamboo and shells like in MNOG II. (Although this may be hard to do. ) You could also do a mining mini-game or something.
Probably MNOG II because it was the first one I played. I also liked the music better and the fact you could buy stuff and collect resources/gems/shells/bamboo/etc (which you couldn't do in the first game).